bm6b00522_si_001.pdf (6.03 MB)
The Effect of Protein Electrostatic Interactions on Globular Protein–Polymer Block Copolymer Self-Assembly
journal contribution
posted on 2016-08-02, 16:58 authored by Christopher
N. Lam, Helen Yao, Bradley D. OlsenMutation
of a superfolder green fluorescent protein (GFP) was used
to design GFP variants with formal net charges of 0, −8, and
−21, providing a set of three proteins in which the total charge
is varied to tune protein–protein interactions while controlling
for the protein size and tertiary structure. After conjugating poly(N-isopropylacrylamide) (PNIPAM) to each of these three GFP
variants, the concentrated solution phase behavior of these three
block copolymers is studied using a combination of small-angle X-ray
scattering (SAXS), depolarized light scattering (DPLS), and turbidimetry
to characterize their morphologies. The electrostatic repulsion between
supercharged GFP suppresses ordering, increasing the order–disorder
transition concentration (CODT) and decreasing
the quality of the ordered nanostructures as measured by the full
width at half-maximum of the primary scattering peak. By contrast,
the charge distribution of the neutrally charged GFP results in its
largest dipole moment, calculated about the protein’s center
of mass, among the three GFP variants and a self-complementary Janus-like
electrostatic surface potential that enhances nanostructure formation.
The different electrostatic properties result in different protein–protein
interactions that affect the high temperature morphologies, including
the formation of macrophase separated or homogeneous micellar phases
and the smaller hexagonal ordering window of the supercharged GFP.
Small improvements in the quality of the ordered nanostructures of
GFP(−21)-PNIPAM can be achieved through protein–divalent
cation interactions. Therefore, varying protein charge and electrostatics
is demonstrated as a method of tuning the magnitude and directionality
of protein–protein interactions to control self-assembly.